R e v i e w s

Solid state physics

Moscow University Physics Bulletin 1991. **46**. N 4. P. 4

The problem of Bragg's X-ray diffraction (XRD) in one-dimensional superlattices (SL) has been studied in detail. A comprehensive review of the publications devoted to this problem is given. A solution of the XRD problem for doped and composite SL with a random modulation law has been obtained in the general form within the kinematic approximation. The effect of the type of a modulating function upon the diffraction spectrum is discussed. In order to solve the problem of the dynamic XRD, we have introduced the concept of the eigen-solutions of the Takagi equations. This has enabled us to use effectively, when studying the problem at hand, the methods of perturbation theory and of slowly varyng amplitudes and to give a thorough analysis of the approximate solutions obtained. Based on the recurrent relations of a new type, the general solution of the problem of XRD in SL is obtained and discussed in various approximations. The exact solution is given for the model of the dynamic XRD in SL with the rectangular modulation. The relation is established between the results obtained with the help of the above methods and those obtained by other authors. The absorption effect is briefly discussed.

Show AbstractR e g u l a r p a p e r s

Theoretical and mathematical physics

Moscow University Physics Bulletin 1991. **46**. N 4. P. 28

A multi-particle wave function for the ground state of magnetized two-dimensional electrons is proposed. The pattern of electron states it gives corresponds to the Wigner two-dimensional lattice. It is also shown that the quantized Hall effect results from spontaneous violation of the translational symmetry of a respective quantum system.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 4. P. 35

The NUT solution to the equations of relativistic gravitation theory is studied. It is shown that the presence of the NUT parameter in the metric of the effective Riemann space results in the appearance of gravitational fields of nonphysical character.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 4. P. 39

The effect of pairwise correlations on the properties of many-particle Fermi systems is studied. The suggested method is a generalization of the density functional method and is based on the representation of the system energy as a functional of the diagonal element of the two-particle density matrix. In this approach the exchange-correlation effects are taken into consideration without including in the model any additional assumptions concerning the properties of these effects.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 4. P. 46

The intensity of massive graviton emission by an arbitrary spatially limited source is found and its positive definiteness shown.

Show AbstractRadiophysics

Moscow University Physics Bulletin 1991. **46**. N 4. P. 51

This paper presents an analysis of a steady-state mode of single-wall and double-wall secondary-emission resonance discharges in a microwave field of a Cerenkov generator with a retardation system in the form of a corrugated (diaphragmed) waveguide and in an electrostatic field of a relativistic electron beam. Relationships have been obtained for the density and thickness of the bunch formed versus parameters of the problem. The power dissipated by the secondary-emission resonance discharge in the surface metal layer is estimated.

Show AbstractOptics and spectroscopy

Moscow University Physics Bulletin 1991. **46**. N 4. P. 58

The problem of synthesis of multilayer optical coatings with a desired amplitude coefficient of reflection of a monochromatic wave is mathematically treated. The general algorithm for designing a multilayer surface film which is optimal with respect to the number of layers and close to optimal with respect to the total thickness, is described. The advantage of such a "quasi-optimum" coating consists in simplicity of its realization.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 4. P. 63

Based on the theory of coupled waves, the amplitude and phase nonreciprocal effects have been investigated for collinear anisotropic diffraction of counter-running light waves on a traveling ultrasonic wave. The investigation results demonstrate the possibility of a substantial decrease in the sensitivity of the amplitude and phase nonreciprocal effects to the variation of the angle of incidence of the light waves on the acoustic line. The results can be used for elaborating new types of amplitude and phase nonreciprocal devices.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 4. P. 67

Processes involved in the formation of associates of molecules of different dyes have been studied. Spectra of such associates have been identified. They consist of two bands shifted relative to the absorption bands of individual molecules toward the long-wave region of the spectrum. It is shown that the binding energy of associated molecules is close to the dispersion interaction energy.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 4. P. 73

This paper analyzes the effect of pulsed radiation of an LGl-505 nitrogen laser on the fluorescence spectra of a dissolved organic substance in water. An extensive set of sample irradiation conditions has been studied to select an optimum regime, in which the photochemical processes cause distortion of the spectrum by no more than 10%.

Show AbstractGeophysics

Moscow University Physics Bulletin 1991. **46**. N 4. P. 77

The turbulence scale distribution in a mixing layer was studied analytically for the purpose of developing methods for computing the energy and mass exchange at the boundaries of flows spreading along solid surfaces. The distributions of the velocity, scale of turbulence, and friction stress were obtained from the system of Reynolds equations. The effect of the cocurrent flow was taken into account. The mixing-length profile, determined analytically for the first time, was similar to the double turbulence microscale curve. Theoretical distributions are in agreement with the measured ones.

Show AbstractAstronomy

Moscow University Physics Bulletin 1991. **46**. N 4. P. 83

It is shown that the external potential of a celestial body of an arbitrary layered structure can be continued analytically inside the body to a certain finite depth depending on the dispersion characteristics of the body surface and density.

Show AbstractSolid state physics

Moscow University Physics Bulletin 1991. **46**. N 4. P. 88

The effect of charging of surface electron states in the $Si—SiO_2$-metal system on the transport of hot electrons from silicon to the oxide level during an avalanche breakdown in silicon has been studied. It is shown that the principal underlying mechanism of this effect is the "integral" change of the electric field produced in the space charge region of the semiconductor by charging the surface states. A new method of determination of the density of surface electron states is proposed. The method is based on measuring the dependence of the electron avalanche injection currents from the semiconductor to the oxide on the amplitude of depleting voltage pulses.

Show AbstractB r i e f r e p o r t s

Radiophysics

Moscow University Physics Bulletin 1991. **46**. N 4. P. 92

The behavior of eigenfields and eigenfrequencies for various operation regimes of layered metal-dielectric microwave systems, including the neighborhood of deflection of the dispersion characteristic, was studied by numerical modeling. The resulting data make it possible to analyze physical processes in waveguide transmission lines and decelerating systems of Cerenkov devices.

Show AbstractGeophysics

Moscow University Physics Bulletin 1991. **46**. N 4. P. 96

The results of experimental measurements of turbulence spectra are discussed. Some deviations from the $k^{-5/3}$ law are observed. A hypothesis of the effect of convective motion on the structure of the turbulent pulsation spectrum is suggested. It is shown that the presence of an additional energy source due to the convective processes results in the transition from the $k^{-5/3}$ law to the $k^{-2}$ law.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 4. P. 99

Examples of typical remote atmosphere probing problems are considered to show that the majority of measurement interpretation problems reduce to calculating a function from an inexactly set argument. The results of a computational experiment lead to the conclusion that in the solution of applied problems it is advisable to apply nonlinear reduction methods.

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